Sunlight Destroys Coronavirus Quickly, Say US Scientists


The new coronavirus is quickly destroyed by sunlight, according to new research announced by a senior US official. (AP)



  • The new coronavirus is quickly destroyed by sunlight, according to new research announced by a senior US official
  • The study has not yet been made public and awaits external evaluation


William Bryan, science and technology advisor to the Department of Homeland Security secretary, told reporters at the White House that government scientists had found ultraviolet rays had a potent impact on the pathogen, offering hope that its spread may ease over the summer.

“Our most striking observation to date is the powerful effect that solar light appears to have on killing the virus, both surfaces and in the air,” he said.

“We’ve seen a similar effect with both temperature and humidity as well, where increasing the temperature and humidity or both is generally less favorable to the virus.”

But the paper itself has not yet been released for review, making it difficult for independent experts to comment on how robust its methodology was.

It has long been known that ultraviolet light has a sterilizing effect, because the radiation damages the virus’s genetic material and their ability to replicate.


A key question, however, will be what the intensity and wavelength of the UV light used in the experiment was and whether this accurately mimics natural light conditions in summer.

“It would be good to know how the test was done, and how the results were measured,” Benjamin Neuman, chair of biological sciences at Texas A&M University-Texarkana, told AFP.

“Not that it would be done badly, just that there are several different ways to count viruses, depending on what aspect you are interested in studying.”



Virus inactivated 

Bryan shared a slide summarizing major findings of the experiment that was carried out at the National Biodefense Analysis and Countermeasures Center in Maryland.

It showed that the virus’s half-life — the time taken for it to reduce to half its amount — was 18 hours when the temperature was 70 to 75 degrees Fahrenheit (21 to 24 degrees Celsius) with 20 percent humidity on a non-porous surface.

This includes things like door handles and stainless steel.

But the half-life dropped to six hours when humidity rose to 80 percent — and to just two minutes when sunlight was added to the equation.

When the virus was aerosolized — meaning suspended in the air — the half-life was one hour when the temperature was 70 to 75 degrees with 20 percent humidity.

In the presence of sunlight, this dropped to just one and a half minutes.

Bryan concluded that summer-like conditions “will create an environment (where) transmission can be decreased.”

He added, though, that reduced spread did not mean the pathogen would be eliminated entirely and social distancing guidelines cannot be fully lifted.

“It would be irresponsible for us to say that we feel that the summer is just going to totally kill the virus and then if it’s a free-for-all and that people ignore those guides,” he said.

Previous work has also agreed that the virus fares better in cold and dry weather than it does in hot and humid conditions, and the lower rate of spread in southern hemisphere countries where it is early fall and still warm bear this out.

Australia, for example, has had just under 7,000 confirmed cases and 77 deaths — well below many northern hemisphere nations.

The reasons are thought to include that respiratory droplets remain airborne for longer in colder weather, and that viruses degrade more quickly on hotter surfaces, because a protective layer of fat that envelops them dries out faster.

US health authorities believe that even if COVID-19 cases slow over summer, the rate of infection is likely to increase again in fall and winter, in line with other seasonal viruses like the flu.



27,08,508 CASES

17,79,729 ACTIVE
7,37,994 RECOVERED
1,90,785 DEATHS
Coronavirus has spread to 185 countries. The total confirmed cases worldwide are 27,08,508 and 1,90,785 have died; 17,79,729 are active cases and 7,37,994 have recovered as on April 24, 2020 at 8:40 am.


23,077 CASES
17,610 ACTIVE
In India, there are 23,077 confirmed cases including 718 deaths. The number of active cases is 17,610 and 4,749 have recovered as on April 24, 2020 at 8:00 am.

State & District Details

S. No. Name of State / UT Total Confirmed cases (Including 77 foreign Nationals) Cured/Discharged/
1 Andaman and Nicobar Islands 22 11 0
2 Andhra Pradesh 895 141 27
3 Arunachal Pradesh 1 1 0
4 Assam 36 19 1
5 Bihar 153 46 2
6 Chandigarh 27 14 0
7 Chhattisgarh 36 28 0
8 Delhi 2376 808 50
9 Goa 7 7 0
10 Gujarat 2624 258 112
11 Haryana 272 156 3
12 Himachal Pradesh 40 18 1
13 Jammu and Kashmir 427 92 5
14 Jharkhand 53 8 3
15 Karnataka 445 145 17
16 Kerala 447 324 3
17 Ladakh 18 14 0
18 Madhya Pradesh 1699 203 83
19 Maharashtra 6430 840 283
20 Manipur 2 2 0
21 Meghalaya 12 0 1
22 Mizoram 1 0 0
23 Odisha 90 33 1
24 Puducherry 7 3 0
25 Punjab 277 65 16
26 Rajasthan 1964 230 27
27 Tamil Nadu 1683 752 20
28 Telangana 960 197 24
29 Tripura 2 1 0
30 Uttarakhand 47 24 0
31 Uttar Pradesh 1510 206 24
32 West Bengal 514 103 15
Total number of confirmed cases in India 23077* 4749 718
*States wise distribution is subject to further verification and reconciliation
*Our figures are being reconciled with ICMR